1. Field of the Invention
The field of the present invention relates generally to implanted devices for tissue stimulation, monitoring, and other therapeutic or diagnostic functions, and specifically to implantable devices for the stimulation of cardiac tissue, for example pacemakers or implantable cardioverter-defibrillators (ICDs). More specifically, it pertains to such devices utilizing wireless energy transfer, for example through ultrasonic means.
2. Description of the Background Art
Conventional wired cardiac pacemaker and defibrillator systems comprise Implantable Pulse Generators (IPGs) configured to be located subcutaneously and connect via leads to stimulator electrodes implanted in the heart. However, because the IPG is connected to leads, the location and surgical process must consider lead insertion into a vascular access.
An ultrasound based wireless cardiac stimulation system has been disclosed in currently pending applications by the applicant (e.g., U.S. patent application Ser. No. 11/315,023). This system employs ultrasonic energy transfer from a subcutaneously implantable controller-transmitter device (C-T), which is directed towards one or more receiver-stimulator (R-S) devices implanted at desired sites in the heart, for example in the left ventricle. Ultrasonic transducers and circuitry in the R-S convert the transmitted ultrasonic energy into electrical energy capable of stimulating the cardiac tissue. The system, C-T, and R-S are described in co-pending U.S. patent applications Nos. (Publication Number) 20060136004, 20060136005, 20070027508, 20070055184, 20070078490 and 20070060961 and Ser. No. 11/752,775, which are herein incorporated by reference in their entirety.
Energy and battery life computations show that the range between the C-T and the R-S has a dramatic impact on the efficiency of energy transfer between them. Therefore, it is desirable to reduce the distance between the C-T and the R-S and thereby improve the efficiency of wireless pacing. An optimal location for cardiac stimulation is believed to be the posterio-lateral LV wall, and an optimal subdermal location for an IPG is the fifth intercostal space. These locations are approximately 10 cm apart. It is desirable to have a cardiac stimulation system that simultaneously optimizes the stimulation location and minimizes the wireless energy delivery range between the C-T and the R-S, thereby providing optimal battery life and optimal stimulation location. The present embodiments provide such a system.